1. Field of the Invention
The present invention relates to a crystal and crystalline solvate of a fluoran compound which are useful as chromogenic compounds in recording materials such as pressure-sensitive and heat-sensitive recording materials, a process for preparation of said crystal and said crystalline solvate, and recording materials comprising said crystal or said crystalline solvate.
2. Description of the Related Art
Pressure-sensitive recording, heat-sensitive recording and electroheat-sensitive recording have conventionally been used as systems for recording transferred information through the mediation of external energy such as pressure, heat or electricity by utilizing a color reaction between a colorless or pale colored electron donor compound (chromogenic compound) and an organic or inorganic electron acceptor (developer).
In these system, fluoran compounds have widely been used as the chromogenic compound.
Many fluoran compounds are known in the prior art, including those having structures of the formulas (A), (B), (C), and (D): ##STR3## Japanese Patent Publication SHO 48-43296(1973) ##STR4## Japanese Patent Publication SHO 48-43296(1973) Japanese Patent Laid-Open Publication SHO 60-202155(1985) ##STR5## Japanese Patent Publication SHO 51-23204(1976) ##STR6## Japanese Patent Laid-Open Publication SHO 61-264058(1986)
However, the compound of the formula (A) has the disadvantage of very low solubility in capsule oil when the compound is used for a pressure-sensitive recording material. Additionally, in the case of applying to the heat-sensitive recording material, the compound itself colors gray to dark gray when mixed with a developer such as bisphenol A and has the defect of providing only a gray to dark gray colored (soiled) paper by applying the compound to the paper.
The color forming temperatures of the compounds having the formulas (B), (C) and (D) are too high to permit their use in a heat-sensitive recording material. Consequently, the performance in these prior art compounds cannot fully meet the present market demand for more rapid and higher density recording. Therefor, a chromogenic compound capable of quickly developing color at lower temperatures has been strongly desired.
Further, the compounds of the formulas (B), (C) and (D) are poorly soluble in capsule oil and their performance is still unsatisfactory for use in the pressure-sensitive recording material.
Japanese Laid-Open Patent SHO 60-47068(1985) discloses fluoran compounds of the formula (I) wherein R.sup.1 is a ##STR7## group, the compound of the formula (I-a), and a ##STR8## group, the compound of the formula (I-b). The compound of the formula (I-b) was described further in detail. ##STR9##
However, the compound of the formula (I-b) which is obtained by precipitating the fluoran compound of the formula (I) from an aqueous methanol solution as described in the patent is substantially amorphous, has low bulk density, scatters in the air during handling, and also has problems on practical use in view of transfer, workability and batching.
The compound of the formula (I-a) obtained by the same process has also low bulk density and is difficult to handle.
Japanese Laid-Open Patent SHO 61-74883(1986) disclosed pressure-sensitive and heat-sensitive recording papers obtained by using the fluoran compounds of the formulas (I-a) and (I-b). However, the description is unsatisfactory for the fluoran compound used and does not distinguish between the amorphous state and the crystal. As mentioned above, the fluoran compounds of the formulas (I-a) and (I-b) which are prepared by the process described in Japanese Laid-Open Patent SHO 60-47068(1985) are substantially amorphous. When heat-sensitive recording papers were prepared by using these amorphous compounds as chromogenic compounds and bisphenol A as a developer, soil was developed on the uncolored portion of the resulting papers and serious problems were liable to occur in practical use.
Japanese Laid-Open Patent SHO 60-141762(1985) suggests fluoran compounds of the formula (I) wherein R.sub.1 is a ##STR10## group, the compound of the formula (I-c), and a ##STR11## group the compound of the formula (I-d). ##STR12##
However, no practical description is found at all on the compounds of the formulas (I-c) and (I-d).
According to the results of experiments, the fluoran compounds of the formulas (I-c) and (I-d) obtained by precipitating, for example, from an aqueous methanol solution were substantially amorphous, had low bulk density, and were difficult to handle.
The heat-sensitive recording sheets using the fluoran compound of the formula (I-d) are also proposed in Japanese Laid-Open Patent SHO 61-74883(1986). However, the description is unsatisfactory for the fluoran compound used and does not distinguish between the amorphous state and the crystal. When heat-sensitive recording papers were prepared by using these amorphous compounds as chromogenic compounds and bisphenol A as a developer, soil was developed on the uncolored portion of the resulting papers and serious problems were liable to occur in practical use.
The crystalline solvates consisting of the fluoran compound of the formula (I) and an aromatic hydrocarbon-based solvent, alcohol-based solvent or ketone-based solvent are not disclosed at all in Japanese Laid-Open Patent SHO 60-47068(1985), 61-74883(1986) and 60-141762(1986).